Burning rate catalysts for solid propellant compositions



3,000,716 BURNING RATE CATALYSTS FOR SOLID PROPEIJLANT COMPOSITIONSRalph W. Lawrence, Glendora, and Gilbert A. Zimmerman, Monrovia, Califi,assignors to Aerojet-General Corporation, Azusa, Califi, a corporationof Ohio No Drawing. Filed June 20, 1955, Ser. No. 516,793 13 Claims.(Cl. 52F.5)

This invention relates to a new burning rate acceleration catalyst forsolid propellant compositions.

Solid, non-metallic propellant compositions are used for rocket andordnance projection, as well as for assisted aircraft take-offs. Suchpropellant compositions are composed essentially of two main components;namely, a combustible organic resin fuel and an oxidizing material. Inuse, such propellants are enclosed within a chamber and ignited wherebylarge quantities of gases are formed. These gases are exhausted throughanorifice thereby giving propulsive force to the vehicle in the oppositedirection.

The fuel component of the propellant needs only to be combustible andpossess physical properties which permit it to be cast or molded into apropellant grain. A wide variety of resins, such as asphalt, polyesters,polyalcohols, polynitroalkenes, and mixtures thereof, are useful forthis purpose.

The oxidizing material is usually an inorganic oxidizing salt. Metalsalts, such as potassium perchlorate, are often used; however, uponcombustion they form solid particles which create large quantities ofvisible smoke. Smoke is highly undesirable for military purposes ofconcealment. Hence, non-smoking, non-metallic, inorganic oxidizing saltssuch as hydrazine and ammonium salts are preferred in such applications.

The desirability of rapid burning propellants for rocket and ordnanceprojections is well established. Metal-con: taining oxidizers generallyprovide fast burning compositions. Unfortunately, propellants utilizingthe nonmetallic, inorganic oxidizing salts as the oxidizer haveheretofore exhibited only relatively slow burning rates. For example,ammonium nitrate oxidized propellants have never been known to burn atrates in excess of 0.1.0

nited States Patent in./sec., even though combusted in the presenceof'burning rate acceleration catalysts such as ammonium dichromate.

We have now found that the burning rates of the highly desirablenon-metallic propellants can be increased as much as 100% byincorporating small amounts of a perchlorate salt of iron, cobalt,chromium, manganese, silver, copper or mixtures thereof in theformulation. These burning rate acceleration catalysts are used in thecompositions in such small amounts, usually from about 0.5% to about 5%by weight of the composition, that the smoke formed by their combustionis negligible. The catalysts of this invention are particularly valuablewhen employed in combination with conventional burning rate accelerationcatalysts such as ammonium dichromate, however, their use is not limitedto this particular embodiment of the invention.

Oxidizers useful in the practice of this invention are non-metallicchlorate, perchlorate, and nitrate salts such as ammonium nitrate,ammonium chlorate, ammonium perchlorate and hydrazine nitrate. Thenon-metallic nitrate salts are preferred due to their availability,stability Patented Sept. 19, 1961 2 and the ease with which they can behandled. The nitrate salts, however, usually do not burn as rapidly asthe chlorate or perchlorate salts.

The-oxidizer, in a finely div1 ed condition, is dispersed throughout thefuel component of the propellant. Ordinarily, the oxidizer is present inan amount of from about 45% to about by weight of the total composition.Optimum results are obtained whenthere is suflicient oxygen in thepropellant to oxidize all of the carbon in the fuel to carbon monoxideand one-third of the hydrogen to Water.

Combustible organic resinous fuels useful in propellant compositions ofthis invention include: asphalt, polymers and copolymers of alkenes,arylalkenes, alkynes, alkenyl diglycols, alkyl alkenoates, alkenylalkanoates, alkenoamides, and amidoalkenyls, and unsaturated alkydresins heteropolymerized with the above compounds. Asphalts havingsoftening points of about 180 F. to about 220 F., and penetration valuesof about 7 to 9 mm./ 5 sec./ gm.- at a temperature of 720 F.,'areusually preferred for rocket fuel due to their ballistic properties.When castability and low expansion coefficients are not essential, othergrades of asphalt can be used. To improve the physical properties of theasphalt, a condensation product of sebacic acid and a polyhydricalcohol, a wax such as cetyl acetamide, or a hydrocarbon oil is oftenincorporated into the asphalt. Suitable fuels of this type are morefully disclosed in assignees copending application Serial No. 634,609,filed December 12, 1945, and assignees United States Patent No.2,565,269, issued August 7, 1951.

.A typical formulation by weight percent of anasphalt base propellantcomposition is as follows:

Propellant composition A Percent Ammonium perchlorate 75.0 Asphalt 10.5Cetyl a'cetamide- 3.0 Castor oil 8.0 Dibutyl seb 3.5 100.0

3 The asphalt-base propellant grains are prepared by heating the asphaltuntil soft, ordinarily about 350 F., stirring in the oxidizers andadditives, and then permitting the mixture to harden inamold'. 1 Y; I

Polyalkenoamides and. amidoalkenyls useful as fuels include:N,N-dimethyl acrylamide, N-methyl acrylamide, N-nitro-N-methylacrylamide, acrylamide N,N-diallyl formamide and N,N-dimethyl vinylcarbamate. Suitable fuels of this type are more fully disclosed inassignees copending application Serial No. 392,472, filed November 16,1953.

, A typical formulation of a propellant composition having a polyamidefuel component is as follows:

Propellant composition B Percent Ammonium nitrate 76.81 N,N-dimethylacrylamide 22.94

Methyl amyl ketone peroxide (polymerization catalyst) p 0.25

The polyamide propellant grain is prepared by mixing A typicalformulation of a propellant composition the amide, oxidizer andpolymerization catalyst until a utilizing an alkyd resin fuel is asfollows: homogeneous mixture is obtained and curing the mixture at atemperature of from about 25 C. to about 100 C. propellant composition EPolyalkenes useful as fuels include: polyisobutylene, 5 Percentbutadiene-styrene copolymers, butadiene-acrylonitrile co- Ammoniumdlfhromate polymers, and isobutylene-isoprene copolymers. SuitableAmmomum mtrate fuels of this type are more fully disclosed in assigneesPolyester by Percent copending application Serial No. 637,004, filedDecem- Percent ber 22, 1945, now abandoned. th glycol 47-00 A typicalformulation of a propellant composition hav- AdlPlF 49-45 ing apolyolefinic fuel component is as follows: Malelc anhydnde Propellantcomposition C 100.00

Percent Styrene 2.66 Ammonium perchlorate 76.00 Methyl acrylate 12.22Copolymer 24.00 Methyl amyl ketone peroxide. 0.49 Percent Cobalt'octoate and lecithin 0.06 Isobutylene 98.5 Isoprene 1.5 100.00

- Another typical formulation is:

Propellant COMPOSIZ'IOII F Ammonium dichromate 2.00

The polyolefin-base propellant grain can be prepared Ammomum ,mtrate76-00 by roll milling the oxidizer into the polyolefin until a Polyesterresm by Percent homogeneous mixture is obtained and then pressing thePercent material into sheets or discs. q 'f q glycol 47'00Polyalkenoates useful as fuels include: polymers and f "j 4945copolymers of acrylic acid, acrylic acid esters, methacrylic Malelcanhydnde acid and methacrylic acid esters. Suitable fuels of this typeare more fully disclosed in assignees copending ap- 100'00 plicationSerial No. 321,943, filed November 21, 1952, Styrene now abandonedMethyl acrylate 12.49

A typical formulation of a propellant composition havfi gl ketonePeroxlde c 1 1 g a polyester fuel component is as follows Cobalt octoaten O- 10 Propellant composition D 4 Percent 100.00 fitiliitifiliiifi21:11:31:11:3::::::::::::: 32:23 The lk prop l ant grams a...preps... by Any] diglycol carbonate 350 blending together the polyesterand olefimc components Methyl methacrylate 10.40 of 1 if g g the P p i ig cata yst. esrre a po ymerlzation ca a ys can a o t Butyl peroxide(polymenzatlon catalysfln be added. The mixture is cast in a mold andthe fuel allouoo lowed to heteropolymerize at a temperature in the rangeof from about 25 C. to about 100 C., and preferably at a temperaturebelow C.

It is preferred to employ a polymerization catalyst to hasten thereaction. The polymerization catalysts usually employed in suchpropellant compositions are organic peroxides such as benzoyl peroxide,lauryl peroxide, acetobenzoyl peroxide, ditertiary butyl peroxide,methyl ethyl ketone peroxide, l-hydroxy-cyclohexyl hydro peroxide,cumene hydroperoxide, and cycloalkane hydrocarbon peroxide, andperesters such as tertiary butyl perbenzoate and diperphthalate.

Various other ingredients can be added for specific pur poses withoutdeparting from the scope of the invention. For example, lecithin can beadded to improve the castability of the uncured propellant. t-Butylcatechol or cobalt 2-ethyl hexanoate is often added as a polymerizationmodifier. l

The propellant grains prepared in the above described manner canwithstand rough handling and will perform satisfactorily at temperaturesin the range of from about F. to about 165 F.

The particular fuel employed in the propellant com- The polyester-basepropellant grain is prepared by mixing the various monomers, oxidizerand polymerization :atalyst until a homogeneous mixture is obtained, and;ubsequently curing the mixture in a mold.

Alkyd resin fuels are polyesters prepared by the conlensation ofpolycarboxylic acid and polyhydric alcohol, me or both of which containsome unsaturation. Among he unsaturated polycarboxylic acids which areordinarily lSed in the preparation of such polyesters are maleic,unraric, citraconic, mesaconic, itaconic acids, etc. laturated acidsfound to be useful include such acids as xalic, malonic, succinic,glutaric, etc. Mixtures of aturated and unsaturated acids are usuallypreferred. he polyhydric alcohols useful are dihyd ric alcohols such sethylene glycol, propylene glycol, glycol, etc.; as well s trihydricalcohols such as glycerol; tetrahydric alcohols lCh as the erythritols;pentahydric alcohols such as rabitol, etc.; or mixtures of any of thesealcohols.

The olefinic component of the fuel can be, for example, yrene, vinylacetate, acrylic acid esters, methacrylic acid ters, allyl compoundssuch as allyl diglycol carbonate, allyl maleate, diallyl diglycollate,and other oefinic position does not aifect the function of the burningrate lmponents such as propylene and butadiene, as well as accelerationcatalyst of this invention. In addition to the e acetylenes. In general,any unsaturated compound propellant compositions described above, thiscatalyst can mpatib'le with the resin, and which will polymerize be usedin compositions utilizing fuel components such as .th it, is suitable;this includes all unsubstituted olefins, polymers of nitroalkenes,nitroalkynes, nitro-containing d in addition, many substituted olefins.Suitable fuels acids and their esters, as well as other combustibleorganic this type are more fully disclosed in assignees copendpolymericmaterials.

; application Serial No. 109,409, filed August 9, 1949. The burning rateacceleration catalysts of this invention are preferably incorporatedinto the propellant compositions in finely divided form and are mixedwith the fuel usually at the same time the oxidizer is mixed. Toillustrate the improvement in the burning rate brought about byincorporating these catalysts into a solid propellant, the results of aseries of burning tests are shown in the table below. These tests weremade using propellant E described above. In the absence of a catalyst,propellant B does not readily sustain combustion, therefore, as a matterof convenience in establishing a burning rate standard for comparativepurposes, amonium dichromate was incorporated in all of the samplegrains. It is to be understood that these examples are presented merelyas a means of illustration and are not intended to limit the scope ofthe invention in any way.

TABLE Percent Burning Catalyst catalyst rate in.

added see- 1,000

psi.

0.07 Chromium perchlorate 1 0.12 Cobalt perchlrate 1 0. 13 Ferrousperchlorate 1 0. 15 Manganese perchlorate. 1 0.13 Silver perchlorate 1O. 12 Copper perchlorate 1 0.11

As can be seen from the data presented in the table above, a substantialincrease in the burning rate of the propellant was efiected by thecatalysts of this invention. Increases in burning rate of the magnitudeherein obtained are particularly valuable in rocketry and ordnanceprojection, for such projectiles are ordinarily guided only during theperiod of their launching. When the full thrust created by thepropellant is available during this time, the projectile can be moreeifectively directed.

Due to the great increase in the burning rates of nonmetallic, smokelesspropellant compositions induced by the above catalysts, and theirapplicability to propellants having a wide variety of fuel components,it is apparent that these catalysts will find extended and valuable usein the field of rocketry and ordnance propulsion.

We claim:

1. A solid, smokeless propellant composition comprising a cured,intimate mixture of from about 45% to about 90% by weight solid,non-metallic, inorganic oxidizing salt, from about to about 35% byweight combustible, organic resin selected from the group consisting of:

(a) asphalt; (b) olefinic polymers;

(0) alkyl alkenoate heteropolymerized with olefin;

(d) unsaturated polyester resin consisting of the con.- densationproduct of saturated polyhydric alcohol and polycarboxylic acidheteropolymerized with an unsaturated compound; and

(e) allrenoamide polymers;

and from about 0.5% to about 5.0% by weight of a burning rateacceleration catalyst selected from the group consisting of theperchlorate salts of iron, cobalt, chromium, manganese, silver, copperand mixtures thereof.

2. The composition of claim 1 wherein the burning rate accelerationcatalyst is chromium perchlorate.

3. The composition of claim 1 wherein the burning rate accelerationcatalyst is cobalt perchlorate.

4. The composition of claim 1 wherein the burning rate accelerationcatalyst is iron perchlorate.

5. The composition of claim 1 wherein the burning rate accelerationcatalyst is manganese perchlorate.

6. The composition of claim 1 wherein the burning rate accelerationcatalyst is silver perchlorate.

7. The composition of claim 1 wherein the burning rate accelerationcatalyst is copper perchlorate.

8. The composition of claim 1 wherein the combustible organic resin isasphalt.

9. The composition of claim 1 wherein the combustible organic resin isan olefinic polymer.

10. The composition of claim 1 wherein the combustitble organic resin isalkyl alkenoate heteropolymerized with an olefin.

11. The composition of claim 1 wherein the combustible organic resin isan unsaturated polyester resin consisting of the condensation product ofsaturated polyhydric alcohol and polycarboxylic acid heteropolymerizedwith an unsaturated compound.

12. The composition of claim 1 wherein the combustible organic resin isan alkenoamide polymer.

13. The composition of claim 1 wherein the non-metallic, inorganicoxidizing salt is selected from the group consisting of nitrate,perchlorate and chlorate salts of ammonia and hydrazine.

'I- riederich et aL: Z. ges. Schiess-Sprengstofiwesen, vol. 21 (1926),pp. 49-52; -87.

1. A SOLID, SMOKELESS PROPELLANT COMPOSITION COMPRISING A CURED,INTIMATE MIXTURE OF FROM ABOUT 45% TO ABOUT 90% BY WEIGHT SOLID,NON-METALLIC, INORGANIC OXIDIZING SALT, FROM ABOUT 10% TO ABOUT 35% BYWEIGHT COMBUSTIBLE, ORGANIC RESIN SELECTED FROM THE GROUP CONSISTING OF:(A) ASPHALT, (B) OLEFINC POLYMERS, (C) ALKYL ALKENOATE HETEROPOLYMERIZEDWITH OLEFIN, (D) UNSATURATED POLYESTER RESIN CONSISTING OF THECONDENSATION PRODUCT OF SATURATED POLYHYDIRC ALCOHOL AND POLYCARBOXYLICACID HETEROPOLYMERIZED WITH AN UNSATURATED COMPOUND, AND (E) ALKENOAMIDEPOLYMERS, AND FROM ABOUT 0.5% BY WEIGHT OF A BURNING RATE ACCELERATIONCATALYST SELECTED FROM THE GROUP CONSISTING OF THE PERCHLORATE SALTS OFIRON, COBALT, CHROMIUM, MANGANESE, SILVER, COPPER AND MIXTURES THEREOF.